Impact-toughness investigations of duplex stainless steels

Duplex stainless steels are very attractive constructional materials for use in aggressive environments because of their several advantages over austenitic stainless steels.Duplex steels have excellent pitting and crevice corrosion resistance, are highly resistant to chloride stress-corrosion cracking and are about twice as strong as common austenitic steels.Better properties are associated with their microstructures consisting of ferrite and austenite grains.However, with certain thermal treatments, these excellent properties may be reduced due to undesired changes in the steel microstructure, related mainly to different solid-state-precipitation processes.The impact toughness of the commercial 2205 duplex stainless steel and the higher-alloy super-duplex 2507 steel was investigated.Both steels were submitted to the ageing treatment in a temperature range between 500 °C and 900 °C with the exposure times of 6 min, 1 h and 10 h; in addition, light microscope examinations, hardness measurements and impact-toughness tests were performed.The main objective of the investigations was to determine the effect of the change in the microstructure on the mechanical properties of the steel.Keywords: duplex stainless steels, heat treatment, impact toughness Dupleksna nerjavna jekla so zanimiv konstrukcijski material za uporabo v agresivnem okolju, ker imajo nekaj prednosti v primerjavi z avstenitnimi nerjavnimi jekli.Dupleksna jekla imajo odli~no odpornost proti jami~asti in {pranjski koroziji, so odporna proti napetostnim korozijskim pokanjem v kloridnem okolju in so okrog dvakrat bolj trdna kot avstenitna nerjavna jekla.Bolj{e lastnosti so povezane z njihovo mikrostrukturo iz zrn ferita in perlita.Vendar pa se njihove odli~ne lastnosti lahko poslab{ajo zaradi ne`elenih sprememb v mikrostrukturi jekla, ki so predvsem v povezavi s procesi izlo~anja iz trdne raztopine.Preiskovana je bila udarna `ilavost komercialnega dupleksnega nerjavnega jekla 2205 in bolj legiranega super dupleksnega jekla 2507.Obe jekli sta bili starani v temperaturnem obmo~ju med 500 °C in 900 °C v trajanju 6 min, 1 h in 10 h.Izvr{ene so bile preiskave s svetlobnim mikroskopom in meritve trdote ter udarne `ilavosti.Glavni namen preiskave je bil dolo~iti vpliv sprememb v mikrostrukturi na mehanske lastnosti jekla.